Determining Breeding Areas and Migration Routes of Coastal Northwest Sooty Fox Sparrows
(Passerella iliaca unalaschcensis) Over-Wintering on Vancouver Island using Geolocators
Summary
The phylogeography of the Fox Sparrow (Passerella iliaca) has been much debated, but birds breeding
along the west coast of North America are generally considered to be a separate species (Passerella
iliaca unalaschecensis) based on mitochondrial DNA. Using plumage characteristics, a further seven subspecies have been identified within this group. These subspecies, and their migration patterns, have
become an emblematic example of leap-frog migration, based upon the early work of Swarth (1920).
However, more recently, these connectivity patterns have been called into question, partly based on the
relative difficulty in accurately distinguishing plumages and subspecies in the field. Light-level geolcators
are now small enough to be carried by <50 g songbirds and can reveal remarkable new insights into
migration patterns and behaviour. Using geolocators, we will track a population of Fox Sparrows
overwintering on southern Vancouver Island to their breeding areas. The objectives of this study are
two-fold: 1) Based on leapfrog patterns identified by Swarth (1920) we will use direct-tracking methods
to test the hypothesis that birds overwintering on Vancouver Island breed on the island and do not mix
with birds along the northwest coast (i.e. strong connectivity) and 2) Identify connections between
overwintering and breeding areas that are important to conservation and management of Fox Sparrow
populations.
Personnel
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Project Leader: Michael Simmons, Rocky Point Bird Observatory (RPBO)
Migration Research Advisor: Dr. Bridget Stutchbury, York University
Science and Geolocator Technical Advisor and Data Analyst: Dr. Kevin Fraser, York University
Vancouver Island Science Advisors:
Bruce Cousens, M.Sc., R.P.Bio., BC Purple Martin Stewardship & Recovery Program, and RPBO,
and
Dr. Jonathan Moran, Royal Roads University and RPBO
Field Leader: Ann Nightingale, RPBO
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Introduction and Background
The Fox Sparrow (Passerella iliaca) is divided into four groups on the basis of mitochondrial DNA and
corresponding plumage characteristics (Zink, 1994). Only one of these groups is found in coastal BC, i.e.,
the Coastal Northwest Sooty Fox Sparrow (P. i. unalaschcensis); within this group seven sub-species are
recognized (Pyle, 1997). Breeding ranges and southward migration to over-wintering areas have been
identified for these sub-species (Swarth, 1920; Figure 1).
Breeding areas are shown with solid blue lines.
Wintering areas are surrounded with dashed lines.
Presumed migration routes link breeding and wintering areas.
P.i. fuliginosa winters within the breeding area
Figure 1: Map from Swarth, 1920
Leap-frog migration in the Sooty Fox Sparrow was first described by Swarth (1920), and the concept was
refined by Bell (1997; Figure 1). Simply put, the most northerly breeders winter the furthest south. The
most southerly breeder (P. i. fuliginosa) breeds in SE Alaska, on the west coast of Vancouver Island and
in immediately adjacent areas of Washington State. The map of leap-frog migration created by Swarth
(1920) shows six sub-species and their migration patterns, Figure 1, above. According to Bell (1997):
“The status of this distribution as the exemplar of leap-frog migration patterns is to some extent
unfortunate because, although there are elements of a leap-frog pattern in this distribution, a
number of factors confound both the leap-frog pattern and its interpretation. For instance, the
breeding areas of populations which winter in southern California are only marginally the most
distant from the wintering area, a fact which is not immediately obvious from the illustration
used in Swarth's (1920) paper, and frequently reproduced elsewhere (e.g., Faaborg 1988, Welty
and Baptista 1988), because of the orthographic projection used. One of these populations, P. i.
unalaschcensis, has a breeding distribution with a latitudinal range similar to that of P. i.
townsendi which winters much further north, and P. i. insularis and most P. i. unalaschcensis
breed to the south of P. i. annectens which also has a relatively northern wintering range.
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Ignoring the three western subspecies, a leap-frog pattern can be discerned among P. i.
annectens, P. i. townsendi and P. i. fuliginosa… “
Bent (1968) describes the difficulty of field identification of the sub-species:
Adjoining races inter-grade wherever their ranges meet, and the differences between some
forms are so slight that the practicality of such fine splitting is sometimes questioned. For
instance George Willett (1933) states his "personal feeling is that we are attempting to recognize
too many races of Passerella and that the situation might be greatly clarified by uniting some of
the most closely allied forms." He suggests that uniting insularis and sinuosa with
unaIaschcensis, "would greatly simplify the classification of the group." Gabrielson and Lincoln
(1959) state: "It is not possible, however, to accurately identify [the Alaskan subspecies] in the
field except as Fox Sparrows. All are large sparrows with dark brown or grayish brown backs with
very heavily streaked under-parts.”
Over-wintering sub-species of Coastal Northwest Sooty Fox Sparrows on Southern Vancouver Island may
include the following:
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P.i. unalaschcensis;
P.i. sinuosa;
P.i. townsendii; and
P.i. fuliginosa.
Linsdale (1928) highlighted variations in the skeletons of these sub-species that appear to be related to
migration:
“In every case the samples with large bones in the wings and pectoral girdle belong to races
which have long migration routes and the samples with those bones weakly developed belong
to relatively sedentary races.”
Differentiation of the sub-species is difficult in the field and in the hand. Wintering birds in southern
Vancouver Island have not been differentiated by RPBO and it is assumed that most of these birds are P.
i. fuliginosa. We do know that almost all Fox Sparrows observed in southern Vancouver Island are of the
Coastal Northwest Sooty group. A very few birds are of the interior Slate-coloured group and very rarely
birds of the Red group are seen (Cruikshank, personal communication). For this project we will only use
birds of the “Sooty” group.
Fox Sparrows can be found throughout the Greater Victoria area during the winter months and are
common in backyards and on the ground near feeding stations. The highest density of Fox Sparrows
recorded during a Christmas Bird Count in the Victoria count circle was 923, and in 2011, the total was
899 (Christmas Bird Counts, Victoria Natural History Society, BC). The closest known breeding area is
about 60km from Victoria, near Shirley, west of Sooke. (BC Breeding Bird Atlas, 2008-2012). These
observations suggest that at the very least, there is a considerable short-distance migration.
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RPBO fall migration records show that there have been 59 returns of Fox Sparrows in later years since
1994. Of the returning birds, 27% return for two years, 15% return for three years, and one bird has
returned and been recaptured for five successive years. In one remarkable year (1998), 16 of the Fox
Sparrows banded returned in subsequent years, including the five-year veteran.
Even though the fall migration monitoring season at Rocky Point ends relatively early for returning Fox
Sparrows, we believe that these birds are returning to use Rocky Point as their wintering area. Evidence
for this assertion is that once Fox Sparrows return, the individual birds are often recaptured several
times. This leads us to believe that they are winter residents rather than transient migrants.
Fox Sparrows as Candidates for Geolocator Use
Southern Vancouver Island is a wintering area for a great number of species that breed elsewhere.
However, the routes by which this concentration of winter species disburse to breeding areas to the
north and east, remain unknown. Significant concentrations of the Coastal Northwest Sooty Fox Sparrow
winter in southern Vancouver Island and this typically west coast species is known to breed over a wide
coastal range to the north (Figure 1). There is no known nesting in the immediate vicinity of Victoria, but
breeding has been reported in other areas of Vancouver Island. The introduction of relatively low cost
geolocators that can be attached safely to smaller birds provides the first opportunity to identify
breeding locations and migration routes for passerines that winter here. If successful, we anticipate
being able to use this approach to identify the migration pathways of many other Pacific coast species.
Survival rates of wintering sparrows, including the Fox Sparrow, were investigated over a period of 13
years at the Coyote Creek Field Station in northern California (Sandercock, B.K., and Jaramillo, A., 2002).
The key findings of this and other studies that have implications for the proposed project are as follows:
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“Winter site fidelity is higher for after hatch year (AHY) birds than for hatch year (HY) birds”;
“Site fidelity of migratory sparrows appears to be flexible among immature birds but becomes
fixed with increasing age”;
“Site fidelity is often strong once a wintering area is selected (Ralph and Mewaldt, 1976)”;
“Immature sparrows of subdominant status may have higher mortality during winter or
subsequent migration periods”;
“Survival rates of sparrows are apparently constant once a bird becomes an adult (Baker et al.,
1981; and Nol and Smith, 1987). Site-faithful individuals have similar rates of local survival in the
six taxa studied, which included Fox Sparrows (0.35); the highest survival was observed in Song
Sparrows (0.56)”; and
“Fidelity to breeding sites is affected by genetic considerations related to mate selection, and by
ecological factors such as local knowledge of food and predator dispersion. In contrast, fidelity
to wintering sites should be determined by ecological factors alone, unless pairing occurs at non
breeding areas, as in waterfowl (Robertson and Cooke, 1998). For at least some migratory land
birds, site attachment is stronger at wintering sites than at breeding areas (Holmes and Sherry,
1992)”.
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In order to access geolocator information, the unit must be recovered after a migration cycle. Therefore,
winter site fidelity is crucial to success. As geolocators are expensive, it is important to deploy them in a
manner that maximizes the likelihood of recovery. We propose the following general approach (details
in the following “methodology” section) for geolocator deployment:
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Fox Sparrow individuals are in their second winter or later;
Geolocator application occurs as late in the winter as possible;
Capture (and recapture) site locations are chosen where repeated observations are easily
achievable throughout the winter; and
Geographically dispersed sites are chosen throughout southern Vancouver Island.
The first geolocators would be attached to over wintering Fox Sparrows in January 2013 and recovered
as soon as possible after the birds return to their wintering areas, in November 2013 or later. Data
analysis would then be possible during the winter of 2013-14.
Geolocator Technology
We propose to use British Antarctic Survey Mk 10S geolocators, with the following geolocator
specifications:
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Size: 18 x 9 x 6 mm
Weight: 1.1 g
Light resolution recording: 10 min.
Harness as described by Fox (2010):
“Studies to date have shown that …. a leg-loop harness based on the Rappole-Tipton harness is
suitable for most terrestrial birds…. Depending on species …. the maximum ratio for back
mounting is considered to be 3-5%”
As the median weight of Fox Sparrows captured at Rocky Point in the fall is 33gm and the total weight of
Mk 10 geolocators and harness is 1.2gm the ratio of backpack weight to bird weight would be 3.6%.
We would use the modified Teflon harness employed for songbird migration research, as reported by
our partners at York University (Stutchbury et al., 2009).
Proposed Methodology
1. Introduction
Fox Sparrows usually return to southern Vancouver Island in October. End of winter departure dates are
not exactly known but are probably in late March and April. While the density in the Greater Victoria
area is high the numbers in any one location are small, suggesting there may be feeding territories
established in the winter. It is believed that the same birds occupy the same territory the entire winter
and occupy the same area in subsequent winters.
It is known that Fox Sparrows average a 35% annual survival rate after hatch year (Sandercock and
Jaramillo, 2000). Also, after the first winter, strong site fidelity is established. We propose therefore to
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select AHY (After Hatch Year) birds in their second or subsequent winters. Birds captured at Rocky Point
are predominantly hatch year birds (> 80%) and we assume that the population of winter resident birds
in southern Vancouver Island is structured similarly. This means a large number of birds will need to be
trapped to obtain sufficient numbers of suitable adult birds.
2. Testing the Harness
It has recently been reported (Seavy, 2011) that seven of eleven (64%) Golden-crowned Sparrows
returned to an over wintering site where geolocators had been attached in good condition but without
the geolocators. It is thought that the kevlar threads of the harness attachment had lost strength due to
exposure to sunlight and/or other atmospheric effects. Although we will use the more sturdy Teflon
harness designed at York University there is a need to test it with Fox Sparrows. Early in the winter, soon
after the birds arrive at overwintering sites, we propose to attach dummy replica geolocators with the
Teflon harnesses and monitor them until early January before attaching geolocators. If the harness
deteriorates we will need to reconsider.
3. Testing for Effects on Performance
We also need to understand whether the attachment of geolocators to birds affects their behavior.
Previous work on other species has not demonstrated any deleterious effect but we believe that
establishing a control group would provide some evidence on whether or not deleterious effects (from
either the geolocator itself or from the backpack) are experienced by Fox Sparrows. This control group
would be colour banded. The control group will only be established if a sufficient number of mature
(AHY – after hatch year) birds are captured.
It has also been proposed that a second control group should be created to test the idea that the ability
of migrating birds to navigate might be affected by steel in the batteries powering the geolocators. This
does not seem to have been a factor in any previous species fitted with geolocators.
To create a control group we have to assume there are sufficient AHY birds available. If there are
insufficient AHY birds available neither control group will be created. If sufficient birds are available we
will use the birds which have been fitted dummy geolocators early in the winter, as a control group. The
decision on whether or not to remove the dummy back packs from these birds will be taken in January.
4. Colour Bands
To track both the geolocator and control group birds during the winter, and to identify returning birds,
colour bands will be installed on all birds.
Three groups will be established:
I.
II.
III.
Birds captured at any time in the project which are determined to be HY (Hatch Year) birds,
AHY birds captured early in the winter and fitted with dummy backpacks (they need to be
recaptured in January to examine the harness condition),
AHY birds fitted with geolocators.
We propose to use fluorescent paint on numbered bands for group (1).
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Group two will have a plastic colour band in addition to the numbered band.
Group three will also have a colour band (different colour !) in addition to the numbered band.
The purpose of the colour banding is to make it easy to identify and recapture birds in each group. There
will not be a unique colour banding scheme for each bird. Once in the hand individuals can of course be
identified by number.
5. Increasing Positional Accuracy
5.1 Parallel measurements from geolocators at fixed locations
Geolocators run in stationary control situations for off-bird static calibration can be surprisingly
accurate when shading effects are eliminated or controlled and daily position estimates are
averaged or otherwise analysed over time. For example, “with about 2 weeks of static precalibration data we have been able to estimate the known static pre-calibration location with a
linear error of <20 km; std. error estimates are on the order of 0.2° lat/long” (Cousens, personal
communication).
Two geolocators will be deployed at fixed locations from the time of installation of geolocators
on birds until the presumed departure time. These two static geolocators may then be deployed
near the presumed west coast Vancouver Island breeding areas for the duration of the breeding
season.
5.2 Avoid dependence on Equinox period
Attach geolocators at least six weeks before the Equinox “black-out” period (March 1 – April 10)
to enable calibration with fixed location geolocators and before the black-out period in which
latitude cannot be accurately determined.
5.3 Live pre-departure downloads
Sun elevations derived from static calibrations are 2-3 degrees lower than when determined
from the bird itself. Live downloads (from birds wearing geolocators) are therefore infinitely
more useful. Assuming the live-download data can be pooled, the advantage is that the sample
size is much greater than if the same data is downloaded when the geolocators are recovered
the following winter. This is because the number of geolocators recovered will likely be about
30% - 40% of all that are installed. As we are uncertain of the effects of re-trapping birds on
several occasions we will leave the live down-load possibility as a desirable but not essential
component of the research.
5.4 Post recovery calibration
A static position accuracy check will be done for a 1-2 week period, off-bird after recovery that
will also confirm low light transition threshold performance free of any cover shading effects.
This presumes the logger is still running.
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6. Sexing the birds
Determining sex by plumage is not possible. Therefore taking blood or feathers is considered. It is
possible that males and females may use different migration routes or, more probably, migrate at
different times. It is also possible that behavioral differences may make positional information from
geolocators on males more accurate than from those on females. Either blood samples or feathers will
be obtained from all birds fitted with geolocators to determine sex and possibly for stable isotope
analysis to determine possible areas of natal origin.
7. Number of Deployment sites
It is preferable to minimize the number of deployment sites to:
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Increase the probability of recovery, and
Reduce the effort required.
However the number of suitable birds at any one site is not large. Fox Sparrows seem to be territorial in
winter (defending feeding habitat). A large proportion of the wintering population is hatch year birds
which have not yet firmly established a wintering site and are not suitable candidates.
During the first winter we need to be able to regularly observe the birds’ behavior with respect to;
tolerance of the harness and dummy backpack, site fidelity, and survival. Later in the winter, after
installation of the geolocators, we also need to continue observing behavior and to record when they
depart, for calibration purposes. When the birds return the deployment sites need close surveillance to
maximize the chance of geolocator recovery and for observation and recapture of control group birds.
We will use backyards with suitable habitat for deployment and we expect only one or, at the most, two
suitable birds at each backyard. As we need dedicated observers rather than adjacent neighbours with
only casual interest, we have defined “site” as an area with a number of dedicated backyards that could
encompass as much as a 20km circle. The proposed Victoria sites are shown in figure 2. Twenty sites
have been tentatively identified in Victoria.
We propose to use two geographically separated sites; Victoria and Nanaimo with 20 geolocators
deployed in Victoria and 10 in Nanaimo. Recoveries in Nanaimo would be expected to be 3 or 4 and
double that number in Victoria, assuming a typical annual survival rate of 35%.
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Figure 2 Proposed Geolocator Deployment Sites in Greater Victoria
Ethical Care and Permits
RPBO holds a banding permit that allows banding of passerines, hummingbirds and owls. It needs to be
extended to include:
Colour banding,
Installation of geolocators,
Capture of birds using ground traps, and
Obtaining blood samples from recaptured birds.
The application has been made to the Bird Banding Office at Environment Canada.
To publish our results, we need certification from an Animal Care Committee. Fox Sparrow and the
Vancouver Island field location will be added to the York University Animal Care Protocol – Number:
2009-2 W (R1).
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